The present invention relates generally to the regeneration of a nitrogen-oxygen compound (NOx) adsorber catalyst. More particularly, the present invention relates to a method of controlling the frequency of NOx adsorber regeneration cycles by modifying a regeneration-triggering variable based on an engine operating condition.
Environmental concerns have led to increasingly stricter regulation of engine emissions by governmental agencies. The reduction of NOx in exhaust emissions from internal combustion engines has become increasingly important in order to meet governmental regulations. It is widely recognized that this trend of stricter government regulation will continue.
Traditional in-cylinder emission reduction techniques such as exhaust gas recirculation and injection rate shaping, by themselves will not be able to achieve the desired low emission levels. Scientists and engineers recognize that aftertreatment technologies will have to be used, and will have to be further developed in order to meet the future low emission requirements of the diesel engine. Abatement of NOx on motor vehicles may be achieved through the use of catalytic technology that converts the NOx species to diatomic nitrogen (N2) using a reductant as shown in the following equation:

Removal of NOx through the use of NOx adsorber catalysts requires that a hydrocarbon reductant be provided to the catalyst to convert the NOx. Typically, on-board fuel (e.g., diesel fuel) is used as the reductant. Fuel is injected into the exhaust stream for reaction with NOx on the catalyst.
Therefore, a need exists for further technological advancements in emission control systems for internal combustion engines. The present invention is directed toward meeting this need.